1. Field of the Invention
This invention relates to convection cooling of high power semiconductor devices and more particularly to microchannel cooling of semiconductor devices formed on a chip of semiconductor material including silicon and silicon carbide.
2. Description of the Prior Art
As the state of the art of semiconductor technology advances and more particularly to those types of devices which are known as power semiconductor devices, and the circuitry associated therewith, there is a continued demand that such devices operate faster and handle more power, while being ever smaller and lower in cost. The semiconductor industry has responded with the development of integrated circuit chips including thereon a large number of transistor devices such as bipolar transistors including power switching devices such as insulated gate bipolar transistors which are particularly applicable for use in medium to high power (1 to 100 kW or more) power converters. Moreover, these devices are currently being incorporated in densely packaged structures that can handle kilowatts of power.
The greatest limitation in the design of such low cost, light weight, high power devices is providing reliable cooling of the densely packaged components. Current state of the art electronic packaging techniques typically utilize redundant parts and excess substrate boundary regions as well as operating the electronics at less than their rated values. For example, in transmitters, silicon RF transistors are typically operated below their power output capability and spaced apart from one another by relatively large separation distances in order to keep them cooled to standardized operating temperatures. The maximum device junction temperature of a silicon bipolar transistor, as dictated by system reliability studies, is normally between 125 and 135.degree. C. The same techniques apply to power switching devices.
More recently, the use of silicon as substrates is being replaced by the use of silicon carbide which can tolerate increased operating temperatures. These devices, however, are still limited internally by known power density and thermal considerations. In conventionally cooled power semiconductors, moreover, the heat generated in a silicon substrate is conducted through several layers of material to an air or liquid cooled heat sink.